1. Field of the Invention
The present invention relates to the field of display, and in particular to a recess structure for print deposition process and manufacturing method thereof.
2. The Related Arts
The organic light emitting diode (OLED) display provides the advantages of self-luminous, low driving voltage, high luminous efficiency, short response time, high clarity and contrast, wide viewing angle of near-180°, wide operating temperature range, enabling flexible display and large full-color display and many other advantages, and is widely recognized as the most potential for the display device development.
OLED display generally comprises: a substrate, an anode disposed on the substrate, a cathode disposed on the anode, and an organic functional layer sandwiched between the anode and the cathode. Wherein the organic functional layer typically comprises a hole transport layer (HTL), an emissive layer (EML), and an electron transport layer (ETL). Each functional layer may be a layer, or more than one layer, e.g., the HTL may be further divided into a hole injection layer (HIL) and a hole transport layer; the ETL may be divided into an electron transport layer and an electron injection layer (EIL). The operating principle behind the OLED display is that the semiconductor materials and organic light emitting material, driven by the electric field, emit light through carrier injection and recombination.
The manufacturing method for OLED display typically starts with forming an anode on a substrate, then forming an HTL on the anode, followed by forming the EML on the HTL, and forming the ETL on the EML, and finally forming a cathode on the ETL, wherein the cathode and the anode are usually made of indium tin oxide (ITO). The functional layers (i.e., HTL, EML, and ETL) are fabricated in a vacuum thermal evaporation process or a solution process.
The so-called solution process is to treat the desired material, such as, dispersing into nano-scale particles and then dissolving in an appropriate solution, and then apply a film formation facility to deposit the solution on a substrate surface, a desired thin film is then formed on the substrate surface after solvent evaporation. Specific ways of film formation can be divided into the ink-jet printing, nozzle printing, roller printing, spin coating, and so on.
The substrate for print deposition process usually is disposed with a recess to restrict the ink. After drying by baking, the ink shrinks in the area restricted by the recess to form a thin film. Refer to FIG. 1, the recess 120 is formed by the enclosure of the dam 110 provided around the substrate 100 and the ITO anode 130. By depositing ink in the recess 120, the HIL 140, the HTL 150 and the EML 160 are formed. Refer to FIG. 2. An inclined angle α≤60° is typically set between the inner circumferential surface of the dam 110 and the upper surface of the substrate 100, and a contact angle θ≥45° is formed between the ink deposited in the recess 120 and the upper surface of the recess 120.
The contact angle between the ink and the inner circumferential inclined surface of the dam 110 has a great influence on the flatness of a film. Refer to FIG. 3. Because the different ink shows different hydrophilic property, ink with good hydrophilic property will climb higher along the inner circumferential inclined surface, resulting in a contact angle θ too small, which leads to poor thickness uniformity of the formed film. When applied in the organic functional layers in the print deposition OLED display, the poor thickness uniformity will cause the intermediate organic functional layer light first, which affects the display effect.